, Jan. 29 -- Dhaka, the densely populated capital of Bangladesh, ranked first among the world's most polluted cities on Thursday morning.

At 9:20 am, Dhaka recorded an air quality index (AQI) score of 257 and classified it as 'very unhealthy' as reported by IQAir.

Cairo in Egypt, Kolkata in India, Ulaanbaatar in Mongolia, and Hanoi in Vietnam occupied the second, third, and fourth spots on the list, with AQI scores of 223, 222, and 199 respectively.

According to the AQI scale, a reading between 50 and 100 is considered 'moderate', with generally acceptable air quality, though sensitive individuals should limit prolonged outdoor exertion.

AQI levels of 101-150 are 'unhealthy for sensitive groups', 151-200 is 'unhealthy', 201-300 is 've...